Evaluation Of Drought Resistance In Two Wild Grasses In Tibet

Drought is one of the most important abiotic stresses in plant growth and development,and the unique environmental conditions in Tibet have led to the growth of various wild grasses with strong drought resistance.Therefore,studying the adaptation mechanisms and drought-resistant traits of wild grasses under drought stress can provide references for the breeding of drought-resistant forage grasses.In this study,two wild forage grasses,Kengiyialia thoroldiana and Trisetum tibeticum,were used as experimental materials,and PEG-6000 was used to simulate drought stress.The changes in seed germination,phenotypic characteristics,and root-shoot physiological and biochemical aspects under drought conditions were investigated,and the physiological and biochemical changes after rehydration were analyzed.The drought resistance of the two wild forage grasses during seed germination and seedling stages was compared using the membership function method.The main research results are as follows:(1)The results of the study showed that as drought increased,the seed germination rate,relative germination rate,germination potential,relative germination potential,germination index,vigor index,drought resistance index,and embryo root and shoot length of Kengiyialia thoroldiana and Trisetum tibeticumall decreased.Both grasses reached their maximum embryo shoot and root lengths at an environmental water potential of-0.04 MPa,while their germination indices reached their lowest values at an environmental water potential of-0.49 MPa.Mild drought stress promoted the growth of the two grasses during the germination stage,while moderate and severe drought stress inhibited their germination.(2)Under drought stress,the plant height,root length,and number of leaves of the two wild forage grasses showed an initial increase followed by a decrease.They reached their maximum values at an environmental water potential of-0.04 MPa.However,the fresh weight,dry weight,and relative water content decreased with the severity of drought stress.They reached their lowest values at an environmental water potential of-0.49 MPa.(3)As drought intensifies and duration extends,the chlorophyll a,chlorophyll b,and total chlorophyll content of two wild grasses generally showed an initial increase followed by a decrease trend.Under all environmental water conditions,the content of chlorophyll a,chlorophyll b,and total chlorophyll gradually increased within 36 hours of drought stress,and then decreased to a minimum at 48 hours.After rehydration treatment,the content of chlorophyll a and total chlorophyll could recover to the control level.The activity of peroxidase,malondialdehyde content,and relative conductivity in both root and shoot of the two grasses showed an overall upward trend during drought stress.At 48 hours of drought stress,under all environmental water conditions,the activity of peroxidase and relative conductivity reached the highest value.The malondialdehyde content showed an initial increase and then a decrease trend under severe stress.After rehydration treatment,the activity of peroxidase,malondialdehyde content,and relative conductivity of the two grasses could recover to the control level.The content of free proline and soluble protein in both root and shoot of the two grasses showed an overall trend of initial increase followed by a decrease with the aggravation of drought stress and the extension of duration,with the content of free proline gradually increasing at 24 hours,while the content of soluble protein increased at 12 hours and then decreased to a minimum at 48 hours.After rehydration treatment,the content of free proline in the roots of the two grasses could recover to the level of the non-stressed treatment,while the content of soluble protein could not fully recover to the level of the non-stressed treatment,indicating that these two grasses have strong drought resistance and recovery ability during the seedling stage.(4)By using the membership function values to comprehensively analyze the germination,growth and physiological indicators of the tested materials,it was found that during the grass germination period,the average membership function value of kengiyialia thoroldiana was the highest,at 0.548.The average membership function value of Trisetum tibeticumwas lower than that of kengiyialia thoroldiana,at 0.437,indicating weaker drought resistance compared to kengiyialia thoroldiana.During the seedling stage,the average membership function value of kengiyialia thoroldiana was 0.476,while that of Trisetum tibeticumwas0.409,indicating that kengiyialia thoroldiana has higher drought resistance during the seedling stage than Trisetum tibeticum.